1. Field of the Invention
This invention relates to a motorized bicycle and, more particularly, relates to a motorized bicycle which has driving power which can be supplied by pedalling only, motor operation only, or a combination of pedalling and motor operation.
2. Prior Art
Motorized bicycles have been designed which include a drive gear driven by either an engine or pedals. Early designs typically included chain or gear mechanisms which were driven by a motor and which were in constant contact with the bicycle's drive sprocket and with the pedals. While these motorized driving mechanisms did provide a means of supplying auxiliary power to a bicycle, they suffered from several disadvantages. For example, the motor and its drive system were typically in direct communication with the pedals at all times, requiring the bicyclist to drive the motor when pedalling. The drag of the motor significantly increased the force needed to pedal the bicycle. Moreover, the drive systems of these early motorized bicycles were extremely difficult to retrofit onto existing bicycles because they required complicated driving arrangements which necessitated extensive modifications of the bicycles onto which they were mounted. As a consequence, these systems could not be used on multi-speed bicycles.
U.S. Pat. No. 2,575,873 to Henney discloses a motorized bicycle which was designed to avoid some of the above-mentioned drawbacks. Henney's bicycle can be powered by pedalling only, by motor operation only, or by a combination of pedalling and motor operation. Henney also discloses the use of a clutch which allows the motor drive unit to be disengaged mechanically from the rear wheel. Once the motor unit is disengaged, the bicycle can be pedalled without the added resistance of the motor drive elements. For example, if the rider desires some light exercise, he can put the clutch in neutral and pedal the bike as if it were non-motorized. While Henney is desirable from this viewpoint, it also has several disadvantages.
First, the location of the motor on the rear wheel as disclosed by Henney results in an unbalanced bicycle because the center of gravity is moved to the rear and because the motor is mounted on one side of the wheel, giving the bike a tendency to fall over to one side. Also, Henney's device is uneconomical to retrofit on existing bicycles, due to the fact that the entire rear wheel of an existing bicycle must be removed and discarded and replaced with the wheel, motor, and transmission assembly disclosed in Henney. If the existing bike is a multi-speed type of say 3, 10, or 15 speeds, then all the gearing associated with the rear wheel will have to be removed and discarded and a special rear wheel installed, which allows only two speeds. Today, multi-speed bicycles are predominant, and the advantage of the multi-speed gearing is lost in a design such as Henney.
U.S. Pat. No. 3,280,932 to Moulton discloses a power-assisted bicycle capable of being pedalled only, powered only, or both pedalled and powered. Through the use of separate chain drives and separate free wheel sprockets on the rear wheel, the Moulton design also allows the bicycle to be pedalled in a free-wheeling mode without the added resistance of the motor drive elements. Moulton is disadvantageous, however, because it requires a separate drive chain and drive gear mounted on the rear wheel, thereby increasing the weight and cost of the system and making it harder to retrofit the same onto existing bicycles. Moreover, even in the free-wheeling mode, the bicycle is noticeably harder to pedal because the pedals must drive the extra gear on the rear wheel, the second drive chain, and the drive gear for the second drive chain.